The present invention relates to a head box in a paper machine.
Heretofore, a head box provided in a paper machine has been known, in which a raw paper liquid is passed through a slice chamber (2) to be ejected from an opening at a slice lip (1) as shown in cross-section in FIG. 1. The raw paper liquid is fed from a preslice chamber (3) through perforations (5) arrayed in a plurality of rows in a perforated plate (4), and enters into the slice chamber (2) which converges in cross-section towards the slice opening as delimited by a top plate (6) and a bottom plate (7). The inner space of the slice chamber (2) is partitioned by flow restraining elements (8) so that a turbulent flow for dispersing fibers may be generated by forming a plurality of restrained flow paths (9). Owing to a hydrodynamic effect of the raw paper liquid flow, the flow restraining elements (8) are held at the positions separated from each other (See Japanese Patent Publication No. 55-6564 (1980)).
FIG. 2 shows another structure of the slice chamber in the prior art, in which flow restraining elements (10) having corrugated surfaces are employed. The flow restraining elements of either configuration can generate a turbulent flow in the raw paper liquid flowing through the restrained flow paths (9) to disperse the fibers of paper.
However, the slice chambers in the head box in the prior art illustrated in FIGS. 1 and 2 had the following shortcoming. That is, although the prior art structures have their characteristic merit that vortexes generated on the upstream side would be quickly reduced in size as they move to the downstream due to the presence of the flow restraining elements and thereby the raw paper liquid can be stably ejected from the slice opening at a uniform rate along the widthwise direction, dispersion of the paper fibers was not sufficient and sometimes it was liable that paper having small flocks was produced.
In addition, in the case of containing long fibers, there exists a tendency that the fibers would align in the direction of the flow, resulting in largely different tensile strengths of the produced paper web between the longitudinal and lateral directions. In general, if a liquid is made to flow in a turbulent flow, vortexes are generated, and when a vortex is produced in the raw paper liquid, a difference in concentration would arise because paper fibers are moved outwardly of the vortex due to a centrifugal force. Furthermore, due to revolution in the vortex, the paper fibers would be subjected to twisting. Accordingly, dispersion of fibers by making use of a turbulent flow was difficult. The present invention has been proposed for the purpose of eliminating the above-mentioned shortcomings in the prior art.